The former France international has acknowledged his players' concentration on domestic matters has been affected by the Champions League clash with the Blues.
Laurent Blanc says Paris-Saint Germain was nowhere near its best in Friday's win at Nice and that a drastic improvement will be required against Chelsea next week.
The reigning French champions stretched their lead at the top of Ligue 1 to 13 points with a 1-0 victory at the Allianz Riviera, but they needed an own goal from Timothee Kolodziejczak to decide a dour affair in their favor.
Blanc was the first to acknowledge PSG had underperformed but argued there were mitigating circumstances, principally his players' preoccupation with the first leg of their Champions League quarterfinal tie with Chelsea at the Parc des Princes on Wednesday night.
"Honestly, this match will not remain in the annals of PSG's history," he told beIN Sport. "But the important thing is that we got the job done. It was not very good, but I think it's still the ninth time we play a league game before the Champions League and, if my stats are correct, this is the ninth victory - and all without conceding goals.
"Great players know that the game before a big one is difficult to manage because subconsciously you think all the time about the big one. But we will need to be more effective against Chelsea. We will need to be very, very, very effective."